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Glennon RA, Dukat M. 1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI): From an Obscure to Pivotal Member of the DOX Family of Serotonergic Psychedelic Agents - A Review. ACS Pharmacol Transl Sci 2024; 7:1722-1745. [PMID: 38898956 PMCID: PMC11184610 DOI: 10.1021/acsptsci.4c00157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2024] [Revised: 04/25/2024] [Accepted: 04/30/2024] [Indexed: 06/21/2024]
Abstract
1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI, or DOX where X = -I) was first synthesized in 1973 in a structure-activity study to explore the effect of various aryl substituents on the then newly identified, and subsequently controlled, hallucinogenic agent 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM, or DOX where X = -CH3). Over time, DOI was found to be a serotonin (5-HT) receptor agonist using various peripheral 5-HT receptor tissue assays and later, following the identification of multiple families of central 5-HT receptors, an agonist at 5-HT2 serotonin receptors in rat and, then, human brain. Today, classical hallucinogens, currently referred to as serotonergic psychedelic agents, are receiving considerable attention for their potential therapeutic application in various neuropsychiatric disorders including treatment-resistant depression. Here, we review, for the first time, the historical and current developments that led to DOI becoming a unique, perhaps a landmark, agent in 5-HT2 receptor research.
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Affiliation(s)
- Richard A. Glennon
- Department of Medicinal Chemistry
School of Pharmacy, Virginia Commonwealth
University, Richmond, Virginia 23298, United States
| | - Małgorzata Dukat
- Department of Medicinal Chemistry
School of Pharmacy, Virginia Commonwealth
University, Richmond, Virginia 23298, United States
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Salinsky LM, Merritt CR, Zamora JC, Giacomini JL, Anastasio NC, Cunningham KA. μ-opioid receptor agonists and psychedelics: pharmacological opportunities and challenges. Front Pharmacol 2023; 14:1239159. [PMID: 37886127 PMCID: PMC10598667 DOI: 10.3389/fphar.2023.1239159] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2023] [Accepted: 09/28/2023] [Indexed: 10/28/2023] Open
Abstract
Opioid misuse and opioid-involved overdose deaths are a massive public health problem involving the intertwined misuse of prescription opioids for pain management with the emergence of extremely potent fentanyl derivatives, sold as standalone products or adulterants in counterfeit prescription opioids or heroin. The incidence of repeated opioid overdose events indicates a problematic use pattern consistent with the development of the medical condition of opioid use disorder (OUD). Prescription and illicit opioids reduce pain perception by activating µ-opioid receptors (MOR) localized to the central nervous system (CNS). Dysregulation of meso-corticolimbic circuitry that subserves reward and adaptive behaviors is fundamentally involved in the progressive behavioral changes that promote and are consequent to OUD. Although opioid-induced analgesia and the rewarding effects of abused opioids are primarily mediated through MOR activation, serotonin (5-HT) is an important contributor to the pharmacology of opioid abused drugs (including heroin and prescription opioids) and OUD. There is a recent resurgence of interest into psychedelic compounds that act primarily through the 5-HT2A receptor (5-HT 2A R) as a new frontier in combatting such diseases (e.g., depression, anxiety, and substance use disorders). Emerging data suggest that the MOR and 5-HT2AR crosstalk at the cellular level and within key nodes of OUD circuitry, highlighting a major opportunity for novel pharmacological intervention for OUD. There is an important gap in the preclinical profiling of psychedelic 5-HT2AR agonists in OUD models. Further, as these molecules carry risks, additional analyses of the profiles of non-hallucinogenic 5-HT2AR agonists and/or 5-HT2AR positive allosteric modulators may provide a new pathway for 5-HT2AR therapeutics. In this review, we discuss the opportunities and challenges associated with utilizing 5-HT2AR agonists as therapeutics for OUD.
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Affiliation(s)
| | | | | | | | - Noelle C. Anastasio
- Center for Addiction Sciences and Therapeutics and Department of Pharmacology and Toxicology, John Sealy School of Medicine, University of Texas Medical Branch, Galveston, TX, United States
| | - Kathryn A. Cunningham
- Center for Addiction Sciences and Therapeutics and Department of Pharmacology and Toxicology, John Sealy School of Medicine, University of Texas Medical Branch, Galveston, TX, United States
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3
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Heal DJ, Gosden J, Smith SL, Atterwill CK. Experimental strategies to discover and develop the next generation of psychedelics and entactogens as medicines. Neuropharmacology 2023; 225:109375. [PMID: 36529260 DOI: 10.1016/j.neuropharm.2022.109375] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Revised: 11/18/2022] [Accepted: 12/08/2022] [Indexed: 12/23/2022]
Abstract
Research on classical psychedelics (psilocybin, LSD and DMT) and entactogen, MDMA, has produced a renaissance in the search for more effective drugs to treat psychiatric, neurological and various peripheral disorders. Psychedelics and entactogens act though interaction with 5-HT2A and other serotonergic receptors and/or monoamine reuptake transporters. 5-HT, which serves as a neurotransmitter and hormone, is ubiquitously distributed in the brain and peripheral organs, tissues and cells where it has vasoconstrictor, pro-inflammatory and pro-nociceptive actions. Serotonergic psychedelics and entactogens have known safety and toxicity risks. For these drugs, the risks been extensively researched and empirically assessed through human experience. However, novel drug-candidates require thorough non-clinical testing not only to predict clinical efficacy, but also to address the risks they pose during clinical development and later after approval as prescription medicines. We have defined the challenges researchers will encounter when developing novel serotonergic psychedelics and entactogens. We describe screening techniques to predict clinical efficacy and address the safety/toxicity risks emerging from our knowledge of the existing drugs: 1) An early-stage, non-clinical screening cascade to pharmacologically characterise novel drug-candidates. 2) Models to detect hallucinogenic activity. 3) Models to differentiate hallucinogens from entactogens. 4) Non-clinical preclinical lead optimisation technology (PLOT) screening to select drug-candidates. 5) Modified animal models to evaluate the abuse and dependence risks of novel psychedelics in Safety Pharmacology testing. Our intention has been to design non-clinical screening strategies that will reset the balance between benefits and harms to deliver more effective and safer novel psychedelics for clinical use. This article is part of the Special Issue on 'National Institutes of Health Psilocybin Research Speaker Series'.
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Affiliation(s)
- D J Heal
- DevelRx Ltd, BioCity, Nottingham, NG1 1GF, UK; Department of Life Sciences, University of Bath, Bath, BA2 7AY, UK.
| | - J Gosden
- DevelRx Ltd, BioCity, Nottingham, NG1 1GF, UK.
| | - S L Smith
- DevelRx Ltd, BioCity, Nottingham, NG1 1GF, UK.
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McClure-Begley TD, Roth BL. The promises and perils of psychedelic pharmacology for psychiatry. Nat Rev Drug Discov 2022; 21:463-473. [PMID: 35301459 DOI: 10.1038/s41573-022-00421-7] [Citation(s) in RCA: 87] [Impact Index Per Article: 43.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/04/2022] [Indexed: 11/09/2022]
Abstract
Psychedelic drugs including psilocybin, N,N'-dimethyltryptamine (DMT) and lysergic acid diethylamide (LSD) are undergoing a renaissance as potentially useful drugs for various neuropsychiatric diseases, with a rapid onset of therapeutic activity. Notably, phase II trials have shown that psilocybin can produce statistically significant clinical effects following one or two administrations in depression and anxiety. These findings have inspired a 'gold rush' of commercial interest, with nearly 60 companies already formed to explore opportunities for psychedelics in treating diverse diseases. Additionally, these remarkable phenomenological and clinical observations are informing hypotheses about potential molecular mechanisms of action that need elucidation to realize the full potential of this investigative space. In particular, despite compelling evidence that the 5-HT2A receptor is a critical mediator of the behavioural effects of psychedelic drugs, uncertainty remains about which aspects of 5-HT2A receptor activity in the central nervous system are responsible for therapeutic effects and to what degree they can be isolated by developing novel chemical probes with differing specificity and selectivity profiles. Here, we discuss this emerging area of therapeutics, covering both controversies and areas of consensus related to the opportunities and perils of psychedelic and psychedelic-inspired therapeutics. We highlight how basic science breakthroughs can guide the discovery and development of psychedelic-inspired medications with the potential for improved efficacy without hallucinogenic or rewarding actions.
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Affiliation(s)
| | - Bryan L Roth
- Department of Pharmacology, University of North Carolina Chapel Hill School of Medicine, Chapel Hill, NC, USA.
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Kojic M, Saelens J, Kadriu B, Zarate CA, Kraus C. Ketamine for Depression: Advances in Clinical Treatment, Rapid Antidepressant Mechanisms of Action, and a Contrast with Serotonergic Psychedelics. Curr Top Behav Neurosci 2022; 56:141-167. [PMID: 35312993 PMCID: PMC10500612 DOI: 10.1007/7854_2022_313] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The approval of ketamine for treatment-resistant depression has created a model for a novel class of rapid-acting glutamatergic antidepressants. Recent research into other novel rapid-acting antidepressants - most notably serotonergic psychedelics (SPs) - has also proven promising. Presently, the mechanisms of action of these substances are under investigation to improve these novel treatments, which also exhibit considerable side effects such as dissociation. This chapter lays out the historical development of ketamine as an antidepressant, outlines its efficacy and safety profile, reviews the evidence for ketamine's molecular mechanism of action, and compares it to the proposed mechanism of SPs. The evidence suggests that although ketamine and SPs act on distinct primary targets, both may lead to rapid restoration of synaptic deficits and downstream network reconfiguration. In both classes of drugs, a glutamate surge activates α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) throughput and increases in brain-derived neurotrophic factor (BDNF) levels. Taken together, these novel antidepressant mechanisms may serve as a framework to explain the rapid and sustained antidepressant effects of ketamine and may be crucial for developing new rapid-acting antidepressants with an improved side effect profile.
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Affiliation(s)
- Marina Kojic
- Department of Pediatrics and Adolescent Medicine, Medical University of Vienna, Vienna, Austria
| | - Johan Saelens
- Department of Psychiatry and Psychotherapy, Medical University of Vienna, Vienna, Austria
| | - Bashkim Kadriu
- Section on the Neurobiology and Treatment of Mood Disorders, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA
- Department of Neuroscience, Janssen Research & Development, LLC, San Diego, CA, USA
| | - Carlos A Zarate
- Section on the Neurobiology and Treatment of Mood Disorders, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA
| | - Christoph Kraus
- Department of Psychiatry and Psychotherapy, Medical University of Vienna, Vienna, Austria.
- Section on the Neurobiology and Treatment of Mood Disorders, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA.
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Re-evaluation of the discriminative stimulus effects of lysergic acid diethylamide with male and female Sprague-Dawley rats. Behav Pharmacol 2021; 31:776-786. [PMID: 32960851 DOI: 10.1097/fbp.0000000000000589] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Recent discoveries from clinical trials with psychedelic-assisted therapy have led to a resurgence of interest in the psychopharmacology of lysergic acid diethylamide (LSD). Preclinical drug discrimination is an invaluable tool to investigate the neurochemical mechanisms underlying subjective drug effects. The current study extends previous drug discrimination research by including both sexes. Adult female (n = 8) and male (n = 8) Sprague-Dawley rats were trained to discriminate 0.08 mg/kg LSD from saline under a fixed ratio 20 schedule of food reinforcement. Substitution tests were conducted with several substances, including other serotonergic hallucinogens, psychostimulants, mixed psychedelic-stimulants and synthetic cathinones. Stimulus antagonist tests were conducted with selected serotonin and dopamine antagonists. LSD-substitution with serotonergic hallucinogens was comparable between sexes. Modest but intriguing differences were observed between male and female rats in the extent of partial substitution by 3,4-methylenedioxymethamphetamine and 3,4-methylenedioxyamphetamine enantiomers and the synthetic cathinones, 3,4-methylenedioxypyrovalerone and 4-methylmethcathinone. Dopamine antagonists failed to block the LSD cue in both sexes and exerted stronger rate suppressant effects in male rats. The 5-hydroxytryptamine antagonist, (R)-(+)-a-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenyl) ethyl]-4-piperidinemethanol (MDL 100 907) blocked LSD discrimination in both sexes, although complete blockade was evident at lower doses in male rats. These results support previous findings regarding the prominent role of serotonergic activities underlying LSDs discriminative stimulus effects in male rats and generalize these findings to female rats. In consideration of the rising popularity in psychedelic-assisted psychotherapy, further research may be warranted to evaluate possible sex differences in the behavioral and subjective effects of LSD.
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Popik P, Krawczyk M, Kuziak A, Bugno R, Hogendorf A, Staroń J, Nikiforuk A. Serotonin type 5A receptor antagonists inhibit D-lysergic acid diethylamide discriminatory cue in rats. J Psychopharmacol 2019; 33:1447-1455. [PMID: 31452444 DOI: 10.1177/0269881119867603] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
PURPOSE Like other psychedelics, D-lysergic acid diethylamide (LSD) affects numerous serotonin receptors, and according to the current dogma, the 5-HT2A receptors are considered the main target for its hallucinogenic effects. LSD, however, also displays agonistic activity at the 5-HT5A receptors, which mediate some of LSD-induced behavioural effects. METHODS Using male Sprague Dawley rats, we examined the effects of 5-HT2A and 5-HT5A receptor antagonists on LSD-induced stimulus control in the two-lever drug discrimination test using a FR10 schedule of reinforcement. RESULTS In animals trained to discriminate 0.08 mg/kg LSD from vehicle 15 minutes after injection, LSD produced dose-related increases in response, with an ED50 (±95% confidence limits) of 0.0384 (± 0.025-0.051) mg/kg). LSD-like responses were observed when the training dose of LSD was given 5-30 but not 90 minutes before the test. Confirming earlier reports, the 5-HT antagonist ketanserin (2 mg/kg) attenuated the LSD response in 50% of rats, and due to pretreatment with 0.2 and 2 mg/kg MDL 100907, 63% and 67% of animals, respectively, failed to select the LSD lever. We then investigated the effects of two 5-HT5A receptor antagonists, and we found that 56% and 60% of rats pretreated with 3 and 10 mg/kg SB 699551, respectively, failed to select the LSD lever. Due to pretreatment with 0.01 mg/kg ASP 5736, 58% of rats did not select the LSD lever. This dose also reduced the response rate but not the number of rats failing to complete the test. CONCLUSIONS The present results suggest that antagonists of the 5-HT5A receptor may inhibit subjective effects of LSD in rats.
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Affiliation(s)
- Piotr Popik
- Behavioral Neuroscience and Drug Development, Maj Institute of Pharmacology, Polish Academy of Sciences, Kraków, Poland
| | - Martyna Krawczyk
- Behavioral Neuroscience and Drug Development, Maj Institute of Pharmacology, Polish Academy of Sciences, Kraków, Poland
| | - Agata Kuziak
- Behavioral Neuroscience and Drug Development, Maj Institute of Pharmacology, Polish Academy of Sciences, Kraków, Poland
| | - Ryszard Bugno
- Department of Medicinal Chemistry, Maj Institute of Pharmacology, Polish Academy of Sciences, Kraków, Poland
| | - Adam Hogendorf
- Department of Medicinal Chemistry, Maj Institute of Pharmacology, Polish Academy of Sciences, Kraków, Poland
| | - Jakub Staroń
- Department of Medicinal Chemistry, Maj Institute of Pharmacology, Polish Academy of Sciences, Kraków, Poland
| | - Agnieszka Nikiforuk
- Behavioral Neuroscience and Drug Development, Maj Institute of Pharmacology, Polish Academy of Sciences, Kraków, Poland
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Johnson MW, Griffiths RR, Hendricks PS, Henningfield JE. The abuse potential of medical psilocybin according to the 8 factors of the Controlled Substances Act. Neuropharmacology 2018; 142:143-166. [PMID: 29753748 PMCID: PMC6791528 DOI: 10.1016/j.neuropharm.2018.05.012] [Citation(s) in RCA: 157] [Impact Index Per Article: 26.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Revised: 04/22/2018] [Accepted: 05/09/2018] [Indexed: 01/09/2023]
Abstract
This review assesses the abuse potential of medically-administered psilocybin, following the structure of the 8 factors of the US Controlled Substances Act (CSA). Research suggests the potential safety and efficacy of psilocybin in treating cancer-related psychiatric distress and substance use disorders, setting the occasion for this review. A more extensive assessment of abuse potential according to an 8-factor analysis would eventually be required to guide appropriate schedule placement. Psilocybin, like other 5-HT2A agonist classic psychedelics, has limited reinforcing effects, supporting marginal, transient non-human self-administration. Nonetheless, mushrooms with variable psilocybin content are used illicitly, with a few lifetime use occasions being normative among users. Potential harms include dangerous behavior in unprepared, unsupervised users, and exacerbation of mental illness in those with or predisposed to psychotic disorders. However, scope of use and associated harms are low compared to prototypical abused drugs, and the medical model addresses these concerns with dose control, patient screening, preparation and follow-up, and session supervision in a medical facility. CONCLUSIONS: (1) psilocybin has an abuse potential appropriate for CSA scheduling if approved as medicine; (2) psilocybin can provide therapeutic benefits that may support the development of an approvable New Drug Application (NDA) but further studies are required which this review describes; (3) adverse effects of medical psilocybin are manageable when administered according to risk management approaches; and (4) although further study is required, this review suggests that placement in Schedule IV may be appropriate if a psilocybin-containing medicine is approved. This article is part of the Special Issue entitled 'Psychedelics: New Doors, Altered Perceptions'.
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Affiliation(s)
- Matthew W Johnson
- Department of Psychiatry and Behavioral Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD, USA.
| | - Roland R Griffiths
- Department of Psychiatry and Behavioral Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD, USA; Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD, USA.
| | - Peter S Hendricks
- Department of Health Behavior, School of Public Health, University of Alabama, Birmingham, AL, USA.
| | - Jack E Henningfield
- Department of Psychiatry and Behavioral Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD, USA; Pinney Associates, Bethesda, MD 20814, USA.
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Mucke HAM. From Psychiatry to Flower Power and Back Again: The Amazing Story of Lysergic Acid Diethylamide. Assay Drug Dev Technol 2016; 14:276-281. [PMID: 27392130 DOI: 10.1089/adt.2016.747] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Among the psychedelic drugs that enjoyed a period of popularity in psychiatric research during the 1950s and 1960s, lysergic acid diethylamide (LSD) is the most prominent one. Psychiatrists of that time had seen LSD not only as a tool for psychotherapy but also as a potential therapeutic for anxiety, depression, alcohol abuse, autism, and even schizophrenia. When it became a quasi-religious epitome of the Hippie counterculture in the mid 1960s, and cases of what we now call hallucinogen persisting perception disorder and acute psychotic "flashbacks" mounted, authorities moved to make LSD illegal. Although research was never actually forbidden, the field almost completely dried out until the early 2010s. Using today's tools of molecular pharmacology, functional imaging, and neuronal network theory, neuropsychiatry is now resurrecting LSD research-with implications that leave us with many medical and ethical questions. Few people are aware that this is a repurposed compound, originally developed in an effort to synthesize a new analeptic. On top of all potential LSD might have in psychiatry, it also serves as a reminder of the unexpected potential that discarded early-stage compounds can have.
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Araújo AM, Carvalho F, Bastos MDL, Guedes de Pinho P, Carvalho M. The hallucinogenic world of tryptamines: an updated review. Arch Toxicol 2015; 89:1151-73. [PMID: 25877327 DOI: 10.1007/s00204-015-1513-x] [Citation(s) in RCA: 118] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Accepted: 03/25/2015] [Indexed: 12/25/2022]
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Halberstadt AL. Recent advances in the neuropsychopharmacology of serotonergic hallucinogens. Behav Brain Res 2015; 277:99-120. [PMID: 25036425 PMCID: PMC4642895 DOI: 10.1016/j.bbr.2014.07.016] [Citation(s) in RCA: 191] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2014] [Revised: 07/07/2014] [Accepted: 07/08/2014] [Indexed: 12/12/2022]
Abstract
Serotonergic hallucinogens, such as (+)-lysergic acid diethylamide, psilocybin, and mescaline, are somewhat enigmatic substances. Although these drugs are derived from multiple chemical families, they all produce remarkably similar effects in animals and humans, and they show cross-tolerance. This article reviews the evidence demonstrating the serotonin 5-HT2A receptor is the primary site of hallucinogen action. The 5-HT2A receptor is responsible for mediating the effects of hallucinogens in human subjects, as well as in animal behavioral paradigms such as drug discrimination, head twitch response, prepulse inhibition of startle, exploratory behavior, and interval timing. Many recent clinical trials have yielded important new findings regarding the psychopharmacology of these substances. Furthermore, the use of modern imaging and electrophysiological techniques is beginning to help unravel how hallucinogens work in the brain. Evidence is also emerging that hallucinogens may possess therapeutic efficacy.
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Affiliation(s)
- Adam L Halberstadt
- Department of Psychiatry, University of California San Diego, La Jolla, CA, United States.
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Barry H, Appel JB. Early preclinical studies of discriminable sedative and hallucinogenic drug effects. Psychopharmacology (Berl) 2009; 203:193-201. [PMID: 18712362 DOI: 10.1007/s00213-008-1292-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2008] [Accepted: 08/01/2008] [Indexed: 10/21/2022]
Abstract
RATIONALE One important technique in behavioral pharmacology is to train laboratory animals to discriminate between a psychoactive drug effect and a nondrug condition. Tests with different drugs have identified several categories of drugs that have different discriminable effects. OBJECTIVES The two authors describe and discuss the early research on discriminable effects of sedative and hallucinogenic drugs and their acquaintance with each other at Yale University prior to their early and frequent publications on discriminable drug effects. Herb Barry studied sedative drugs primarily and Jim Appel studied hallucinogenic drugs. RESULTS Sedative drugs include ethyl alcohol, barbiturates, and benzodiazepines. Their discriminable effects are largely attributable to the activation of an inhibitory neurotransmitter, gamma-amino butyric acid. Alcohol has the most pervasive effect in accordance with the high dose required to alter behavior. Hallucinogenic drugs include lysergic acid diethylamide and mescaline. They increase the activity of the neurotransmitter 5-hydroxytryptamine and, perhaps, dopamine in the central nervous system (CNS). In spite of their relatively low concentrations in the brain, both of these neurotransmitters have many important behavioral effects. CONCLUSIONS Various sedative drugs cause a discriminable decrease in the function of the CNS. Different types of sedatives can be discriminated from each other. Indole and phenylethylamine hallucinogens have potent discriminative stimulus properties, which are related to the actions of biogenic amine neurotransmitters in the CNS.
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Schultz DM, Prescher JA, Kidd S, Marona-Lewicka D, Nichols DE, Monte A. 'Hybrid' benzofuran-benzopyran congeners as rigid analogs of hallucinogenic phenethylamines. Bioorg Med Chem 2008; 16:6242-51. [PMID: 18467103 PMCID: PMC2601679 DOI: 10.1016/j.bmc.2008.04.030] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2008] [Accepted: 04/14/2008] [Indexed: 10/22/2022]
Abstract
Phenylalkylamines that possess conformationally rigidified furanyl moieties in place of alkoxy arene ring substituents have been shown previously to possess the highest affinities and agonist functional potencies at the serotonin 5-HT(2A) receptor among this chemical class. Further, affinity declines when both furanyl rings are expanded to the larger dipyranyl ring system. The present paper reports the synthesis and pharmacological evaluation of a series of 'hybrid' benzofuranyl-benzopyranyl phenylalkylamines to probe further the sizes of the binding pockets within the serotonin 5-HT(2A) agonist binding site. Thus, 4(a-b), 5(a-b), and 6 were prepared as homologs of the parent compound, 8-bromo-1-(2,3,6,7-tetrahydrobenzo[1,2-b:4,5-b']difuran-4-yl)-2-aminopropane 2, and their affinity, functional potency, and intrinsic activity were assessed using cells stably expressing the rat 5-HT(2A) receptor. The behavioral pharmacology of these new analogs was also evaluated in the two-lever drug discrimination paradigm. Although all of the hybrid isomers had similar, nanomolar range receptor affinities, those with the smaller furanyl ring at the arene 2-position (4a-b) displayed a 4- to 15-fold greater functional potency than those with the larger pyranyl ring at that position (5a-b). When the furan ring of the more potent agonist 4b was aromatized to give 6, a receptor affinity similar to the parent difuranyl compound 2 was attained, along with a functional potency equivalent to 2, 4a, and 4b. In drug discrimination experiments using rats trained to discriminate LSD from saline, 4b was more than two times more potent than 5b, with the latter having a potency similar to the classic hallucinogenic amphetamine 1 (DOB).
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Affiliation(s)
- Danielle M. Schultz
- Department of Chemistry, University of Wisconsin-La Crosse, 1725 State Street, La Crosse, Wisconsin 54601
| | - Jennifer A. Prescher
- Department of Chemistry, University of Wisconsin-La Crosse, 1725 State Street, La Crosse, Wisconsin 54601
| | - Stephanie Kidd
- Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmaceutical Sciences, Purdue University, West Lafayette, Indiana 47907
| | - Danuta Marona-Lewicka
- Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmaceutical Sciences, Purdue University, West Lafayette, Indiana 47907
| | - David E. Nichols
- Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmaceutical Sciences, Purdue University, West Lafayette, Indiana 47907
| | - Aaron Monte
- Department of Chemistry, University of Wisconsin-La Crosse, 1725 State Street, La Crosse, Wisconsin 54601
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Li JX, Rice KC, France CP. Discriminative stimulus effects of 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane in rhesus monkeys. J Pharmacol Exp Ther 2008; 324:827-33. [PMID: 17993605 DOI: 10.1124/jpet.107.130625] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Discriminative stimulus effects of 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM) and related drugs have been studied extensively in rodents, although the generality of those findings across species is not known. The goals of this study were to see whether monkeys could discriminate DOM and to characterize the DOM discriminative stimulus by studying a variety of drugs, including those with hallucinogenic activity in humans. Four rhesus monkeys discriminated between 0.32 mg/kg s.c. DOM and vehicle after an average of 116 (range = 85-166) sessions while responding under a fixed ratio 5 schedule of stimulus shock termination. Increasing doses of DOM occasioned increased responding on the drug lever with the training dose occasioning DOM-lever responding for up to 2 h. The serotonin (5-HT)(2A/2C) receptor antagonists ritanserin and ketanserin, the 5-HT(2A) receptor antagonist (+)2,3-dimethoxyphenyl-1-[2-(4-piperidine)-methanol] (MDL100907), and its (-)stereoisomer MDL100009 [(-)2,3-dimethoxyphenyl-1-[2-(4-piperidine)-methanol], but not haloperidol, completely blocked the discriminative stimulus effects of DOM. Quipazine as well as several drugs with hallucinogenic activity in humans, including (+)lysergic acid diethylamide, (-)DOM, and 2,5-dimethoxy-4-(n)-propylthiophenethylamine (2C-T-7), occasioned DOM-lever responding. The kappa-opioid receptor agonists U-50488 and salvinorin A (a hallucinogen) did not exert DOM-like effects and neither did ketamine, phencyclidine, amphetamine, methamphetamine, cocaine, morphine, yohimbine, fenfluramine, 8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT), or (+/-)-2-(N-phenethyl-N-1'-propyl)amino-5-hydroxytetralin hydrochloride (N-0434). These data confirm in nonhuman primates a prominent role for 5-HT(2A) receptors in the discriminative stimulus effects of some drugs with hallucinogenic activity in humans. The failure of another drug with hallucinogenic activity (salvinorin A) to substitute for DOM indicates that different classes of hallucinogens exert qualitatively different discriminative stimulus effects in nonhumans.
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Affiliation(s)
- Jun-Xu Li
- Department of Pharmacology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA
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16
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Krall CM, Richards JB, Rabin RA, Winter JC. Marked decrease of LSD-induced stimulus control in serotonin transporter knockout mice. Pharmacol Biochem Behav 2007; 88:349-57. [PMID: 17935763 DOI: 10.1016/j.pbb.2007.09.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/22/2007] [Revised: 09/06/2007] [Accepted: 09/07/2007] [Indexed: 02/05/2023]
Abstract
RATIONALE Based upon extensive studies in the rat, it has been suggested that stimulus control by LSD is mediated by 5-HT2A receptors, with serotonergic receptors of the 5-HT1A and 5-HT2C subtypes playing modulatory roles. In genetically modified mice lacking the serotonin transporter (SERT), 5-HT2A receptor density is decreased and, at a functional level, the head-twitch response following the administration of DOI, an index of activation of 5-HT2A receptors, is reduced. Taken together, these studies led us to hypothesize that the efficacy of LSD in establishing stimulus control is diminished or abolished in mice lacking the serotonin transporter. OBJECTIVE Determine the efficacy of LSD for establishing stimulus control in SERT knockout (KO) mice. METHODS SERT KO mice and wildtype (WT) littermates were trained in a visual discrimination on a progressive fixed ratio (FR) water-reinforced task and subsequently trained on a FR10 schedule with LSD (0.17 or 0.30 mg/kg) or vehicle. To control for general deficiencies in drug discrimination, mice were trained with pentobarbital (15 or 30 mg/kg) or vehicle. RESULTS The visual stimulus exerted control in both genotypes. LSD-induced stimulus control in 90% of WT mice but only 31% of SERT KO mice. In contrast, pentobarbital-induced stimulus control in 80% of WT mice and 54% of knockout mice. CONCLUSIONS Although SERT KO mice exhibited stimulus control by the non-serotonergic drug, pentobarbital, the efficacy of LSD in these animals was markedly decreased, suggesting that reduced density of 5-HT1A and/or 5-HT2A receptors underlies the absence of stimulus control by LSD.
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Affiliation(s)
- C M Krall
- Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, University at Buffalo, 102 Farber Hall, SUNY-Buffalo, NY 14214-3000, USA
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17
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Winter JC, Rice KC, Amorosi DJ, Rabin RA. Psilocybin-induced stimulus control in the rat. Pharmacol Biochem Behav 2007; 87:472-80. [PMID: 17688928 PMCID: PMC2000343 DOI: 10.1016/j.pbb.2007.06.003] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/12/2007] [Revised: 06/05/2007] [Accepted: 06/11/2007] [Indexed: 11/28/2022]
Abstract
Although psilocybin has been trained in the rat as a discriminative stimulus, little is known of the pharmacological receptors essential for stimulus control. In the present investigation rats were trained with psilocybin and tests were then conducted employing a series of other hallucinogens and presumed antagonists. An intermediate degree of antagonism of psilocybin was observed following treatment with the 5-HT(2A) receptor antagonist, M100907. In contrast, no significant antagonism was observed following treatment with the 5-HT(1A/7) receptor antagonist, WAY-100635, or the DA D(2) antagonist, remoxipride. Psilocybin generalized fully to DOM, LSD, psilocin, and, in the presence of WAY-100635, DMT while partial generalization was seen to 2C-T-7 and mescaline. LSD and MDMA partially generalized to psilocybin and these effects were completely blocked by M-100907; no generalization of PCP to psilocybin was seen. The present data suggest that psilocybin induces a compound stimulus in which activity at the 5-HT(2A) receptor plays a prominent but incomplete role. In addition, psilocybin differs from closely related hallucinogens such as 5-MeO-DMT in that agonism at 5-HT(1A) receptors appears to play no role in psilocybin-induced stimulus control.
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Affiliation(s)
- J C Winter
- Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, University at Buffalo, 102 Farber Hall, Buffalo, NY 14214-3000, USA.
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18
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Marona-Lewicka D, Nichols DE. Further evidence that the delayed temporal dopaminergic effects of LSD are mediated by a mechanism different than the first temporal phase of action. Pharmacol Biochem Behav 2007; 87:453-61. [PMID: 17618679 DOI: 10.1016/j.pbb.2007.06.001] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/23/2007] [Revised: 06/03/2007] [Accepted: 06/04/2007] [Indexed: 11/16/2022]
Abstract
Activation of 5-HT(2A) receptors is thought to mediate the hallucinogenic effects of LSD. Nevertheless, in a previous report we provided evidence that a delayed temporal phase of the behavioral pharmacology of LSD is mediated by D(2)-like dopamine receptor stimulation. In this study rats were trained to discriminate LSD with either a 30 min preinjection time (LSD-30, N=12) or a 90 min preinjection time (LSD-90, N=13) from saline, using a two-lever, food-reinforced operant conditioning task. We then tested a large number of agonists and antagonists belonging to distinct pharmacological classes in these animals. As anticipated, classical hallucinogens such as psilocin and mescaline substituted only in LSD-30 rats, and not in LSD-90 rats. The dopamine receptor agonists ABT-724, aripiprazole, dihydrexidine, WAY 100635, and SKF 38393, fully or partially mimicked LSD-90, but not LSD-30. The results reported here support and extend our previous conclusion that the delayed temporal effects of LSD are mediated by activation of a dopaminergic system.
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Affiliation(s)
- Danuta Marona-Lewicka
- Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmaceutical Sciences, RHPH, 575 Stadium Mall Dr. Purdue University, West Lafayette, IN 47907-2091, United States
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19
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Krebs-Thomson K, Ruiz EM, Masten V, Buell M, Geyer MA. The roles of 5-HT1A and 5-HT2 receptors in the effects of 5-MeO-DMT on locomotor activity and prepulse inhibition in rats. Psychopharmacology (Berl) 2006; 189:319-29. [PMID: 17013638 DOI: 10.1007/s00213-006-0566-1] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/04/2006] [Accepted: 08/13/2006] [Indexed: 12/01/2022]
Abstract
RATIONALE The hallucinogen 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) is structurally similar to other indoleamine hallucinogens such as LSD. The present study examined the effects of 5-MeO-DMT in rats using the Behavioral Pattern Monitor (BPM), which enables analyses of patterns of locomotor activity and exploration, and the prepulse inhibition of startle (PPI) paradigm. OBJECTIVES A series of interaction studies using the serotonin (5-HT)(1A) antagonist WAY-100635 (1.0 mg/kg), the 5-HT(2A) antagonist M100907 (1.0 mg/kg), and the 5-HT(2C) antagonist SER-082 (0.5 mg/kg) were performed to assess the respective contributions of these receptors to the behavioral effects of 5-MeO-DMT (0.01, 0.1, and 1.0 mg/kg) in the BPM and PPI paradigms. RESULTS 5-MeO-DMT decreased locomotor activity, investigatory behavior, the time spent in the center of the BPM chamber, and disrupted PPI. All of these effects were antagonized by WAY-100635 pretreatment. M100907 pretreatment failed to attenuate any of these effects, while SER-082 pretreatment only antagonized the PPI disruption produced by 5-MeO-DMT. CONCLUSIONS While the prevailing view was that the activation of 5-HT(2) receptors is solely responsible for hallucinogenic drug effects, these results support a role for 5-HT(1A) receptors in the effects of the indoleamine hallucinogen 5-MeO-DMT on locomotor activity and PPI in rats.
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Affiliation(s)
- Kirsten Krebs-Thomson
- Department of Psychiatry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0804, USA
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20
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Gresch PJ, Barrett RJ, Sanders-Bush E, Smith RL. 5-Hydroxytryptamine (serotonin)2A receptors in rat anterior cingulate cortex mediate the discriminative stimulus properties of d-lysergic acid diethylamide. J Pharmacol Exp Ther 2006; 320:662-9. [PMID: 17077317 DOI: 10.1124/jpet.106.112946] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
d-Lysergic acid diethylamide (LSD), an indoleamine hallucinogen, produces profound alterations in mood, thought, and perception in humans. The brain site(s) that mediates the effects of LSD is currently unknown. In this study, we combine the drug discrimination paradigm with intracerebral microinjections to investigate the anatomical localization of the discriminative stimulus of LSD in rats. Based on our previous findings, we targeted the anterior cingulate cortex (ACC) to test its involvement in mediating the discriminative stimulus properties of LSD. Rats were trained to discriminate systemically administered LSD (0.085 mg/kg s.c.) from saline. Following acquisition of the discrimination, bilateral cannulae were implanted into the ACC (AP, +1.2 mm; ML, +/-1.0 mm; DV, -2.0 mm relative to bregma). Rats were tested for their ability to discriminate varying doses of locally infused LSD (0.1875, 0.375, and 0.75 microg/side) or artificial cerebrospinal fluid (n = 3-7). LSD locally infused into ACC dose-dependently substituted for systemically administered LSD, with 0.75 microg/side LSD substituting completely (89% correct). Systemic administration of the selective 5-hydroxytryptamine (serotonin) (5-HT)(2A) receptor antagonist R-(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidine-methanol (M100907; 0.4 mg/kg) blocked the discriminative cue of LSD (0.375 microg/side) infused into ACC (from 68 to 16% drug lever responding). Furthermore, M100907 (0.5 microg/microl/side) locally infused into ACC completely blocked the stimulus effects of systemic LSD (0.04 mg/kg; from 80 to 12% on the LSD lever). Taken together, these data indicate that 5-HT(2A) receptors in the ACC are a primary target mediating the discriminative stimulus properties of LSD.
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Affiliation(s)
- Paul J Gresch
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
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21
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Fantegrossi WE, Harrington AW, Kiessel CL, Eckler JR, Rabin RA, Winter JC, Coop A, Rice KC, Woods JH. Hallucinogen-like actions of 5-methoxy-N,N-diisopropyltryptamine in mice and rats. Pharmacol Biochem Behav 2006; 83:122-9. [PMID: 16460788 DOI: 10.1016/j.pbb.2005.12.015] [Citation(s) in RCA: 120] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/02/2005] [Revised: 12/07/2005] [Accepted: 12/29/2005] [Indexed: 11/15/2022]
Abstract
Few studies have examined the effects of 5-methoxy-N,N-diisopropyltryptamine (5-MeO-DIPT) in vivo. In these studies, 5-MeO-DIPT was tested in a drug-elicited head twitch assay in mice where it was compared to the structurally similar hallucinogen N,N-dimethyltryptamine (N,N-DMT) and challenged with the selective serotonin (5-HT)2A antagonist M100907, and in a lysergic acid diethylamide (LSD) discrimination assay in rats where its subjective effects were challenged with M100907 or the 5-HT 1A selective antagonist WAY-100635. Finally, the affinity of 5-MeO-DIPT for three distinct 5-HT receptors was determined in rat brain. 5-MeO-DIPT, but not N,N-DMT, induced the head twitch responses in the mouse, and this effect was potently antagonized by prior administration of M100907. In rats trained with LSD as a discriminative stimulus, there was an intermediate degree (75%) of generalization to 5-MeO-DIPT and a dose-dependent suppression of response rates. These interoceptive effects were abolished by M100907, but were not significantly attenuated by WAY-100635. Finally, 5-MeO-DIPT had micromolar affinity for 5-HT 2A and 5-HT 2C receptors, but much higher affinity for 5-HT 1A receptors. 5-MeO-DIPT is thus effective in two rodent models of 5-HT2 agonist activity, and has affinity at receptors relevant to hallucinogen effects. The effectiveness with which M100907 antagonizes the behavioral actions of this compound, coupled with the lack of significant antagonist effects of WAY-100635, strongly suggests that the 5-HT 2A receptor is an important site of action for 5-MeO-DIPT, despite its apparent in vitro selectivity for the 5-HT 1A receptor.
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MESH Headings
- 5-Methoxytryptamine/analogs & derivatives
- 5-Methoxytryptamine/pharmacokinetics
- 5-Methoxytryptamine/pharmacology
- Animals
- Brain/drug effects
- Brain/metabolism
- Dose-Response Relationship, Drug
- Fluorobenzenes/pharmacology
- Hallucinogens/pharmacology
- Lysergic Acid Diethylamide/pharmacology
- Male
- Mice
- Piperazines/pharmacology
- Piperidines/pharmacology
- Pyridines/pharmacology
- Rats
- Rats, Inbred F344
- Receptor, Serotonin, 5-HT1A/drug effects
- Receptor, Serotonin, 5-HT1A/metabolism
- Receptor, Serotonin, 5-HT2A/drug effects
- Receptor, Serotonin, 5-HT2A/metabolism
- Serotonin Antagonists/pharmacology
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Affiliation(s)
- W E Fantegrossi
- Division of Neuroscience, Yerkes National Primate Research Center, Emory University, 954 Gatewood Road, Atlanta, GA 30322, USA.
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22
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Winter JC, Kieres AK, Zimmerman MD, Reissig CJ, Eckler JR, Ullrich T, Rice KC, Rabin RA, Richards JB. The stimulus properties of LSD in C57BL/6 mice. Pharmacol Biochem Behav 2005; 81:830-7. [PMID: 16005500 PMCID: PMC1351004 DOI: 10.1016/j.pbb.2005.05.014] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/06/2004] [Revised: 02/07/2005] [Accepted: 05/19/2005] [Indexed: 11/22/2022]
Abstract
RATIONALE Drug-induced stimulus control has proven to be a powerful tool for the assessment of a wide range of psychoactive drugs. Although a variety of species has been employed, the majority of studies have been in the rat. However, with the development of techniques which permit the genetic modification of mice, the latter species has taken on new importance. Lysergic acid diethylamide [LSD], the prototypic indoleamine hallucinogen, has not previously been trained as a discriminative stimulus in mice. OBJECTIVE To demonstrate the feasibility of LSD-induced stimulus control in the mouse and to provide a preliminary characterization of the stimulus properties of LSD in that species. METHODS Male C57BL/6 mice were trained using a left or right nose-poke operant on a fixed ratio 10, water reinforced task following the injection of lysergic acid diethylamide [LSD, 0.17 or 0.30 mg/kg, s.c.; 15 min pretreatment] or vehicle. RESULTS Stimulus control was established in 6 of 16 mice at a dose of LSD of 0.17 mg/kg after 39 sessions. An increase in dose to 0.30 mg/kg for the remaining mice resulted in stimulus control in an additional 5 subjects. In the low dose group, subsequent experiments demonstrated an orderly dose-effect relationship for LSD and a rapid offset of drug action with an absence of LSD effects 60 min after injection. When LSD [0.17 mg/kg] was administered in combination with the selective 5-HT2A antagonist, M100907, LSD-appropriate responding was significantly but incompletely reduced to approximately 50%; concurrently, response rates declined significantly. In mice trained with a dose of LSD of 0.30 mg/kg, full generalization to the phenethylamine hallucinogen, [-]-2,5-dimethoxy-4-methylamphetamine [DOM] was observed. CONCLUSIONS The present data demonstrate the feasibility of LSD-induced stimulus control in the mouse. The general features of stimulus control by LSD in the mouse closely resemble those observed in the rat but the present data suggest that there may be significant differences as well.
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Affiliation(s)
- J C Winter
- Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, University at Buffalo, 102 Farber Hall, Buffalo, NY 14214-3000, USA.
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23
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Reissig CJ, Eckler JR, Rabin RA, Winter JC. The 5-HT1A receptor and the stimulus effects of LSD in the rat. Psychopharmacology (Berl) 2005; 182:197-204. [PMID: 16025319 PMCID: PMC1266303 DOI: 10.1007/s00213-005-0068-6] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2004] [Accepted: 05/10/2005] [Indexed: 10/25/2022]
Abstract
RATIONALE It has been suggested that the 5-HT1A receptor plays a significant modulatory role in the stimulus effects of the indoleamine hallucinogen lysergic acid diethylamide (LSD). OBJECTIVE The present study sought to characterize the effects of several compounds with known affinity for the 5-HT1A receptor on the discriminative stimulus effects of LSD. METHODS Twelve male Fischer 344 rats were trained in a two-lever, fixed-ratio (FR) 10, and food-reinforced task with LSD (0.1 mg/kg, i.p.; 15-min pretreatment) as a discriminative stimulus. Combination and substitution tests with the 5-HT(1A) agonists, 8-OH-DPAT, buspirone, gepirone, and ipsapirone, with LSD-induced stimulus control were then performed. The effects of these 5-HT1A ligands were also tested in the presence of the selective 5-HT1A receptor antagonist, WAY-100,635 (0.3 mg/kg, s.c.; 30-min pretreatment). RESULTS In combination tests, stimulus control by LSD was increased by all 5-HT1A receptor ligands with agonist properties. Similarly, in tests of antagonism, the increase in drug-appropriate responding caused by stimulation of the 5-HT1A receptor was abolished by administration of WAY-100,635. CONCLUSION These data, obtained using a drug discrimination model of the hallucinogenic effects of LSD, provide support for the hypothesis that the 5-HT1A receptor has a significant modulatory role in the stimulus effects of LSD.
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Affiliation(s)
- C J Reissig
- Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, Buffalo, NY, USA.
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24
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Gresch PJ, Smith RL, Barrett RJ, Sanders-Bush E. Behavioral tolerance to lysergic acid diethylamide is associated with reduced serotonin-2A receptor signaling in rat cortex. Neuropsychopharmacology 2005; 30:1693-702. [PMID: 15756304 DOI: 10.1038/sj.npp.1300711] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Tolerance is defined as a decrease in responsiveness to a drug after repeated administration. Tolerance to the behavioral effects of hallucinogens occurs in humans and animals. In this study, we used drug discrimination to establish a behavioral model of lysergic acid diethylamide (LSD) tolerance and examined whether tolerance to the stimulus properties of LSD is related to altered serotonin receptor signaling. Rats were trained to discriminate 60 microg/kg LSD from saline in a two-lever drug discrimination paradigm. Two groups of animals were assigned to either chronic saline treatment or chronic LSD treatment. For chronic treatment, rats from each group were injected once per day with either 130 microg/kg LSD or saline for 5 days. Rats were tested for their ability to discriminate either saline or 60 microg/kg LSD, 24 h after the last chronic injection. Rats receiving chronic LSD showed a 44% reduction in LSD lever selection, while rats receiving chronic vehicle showed no change in percent choice on the LSD lever. In another group of rats receiving the identical chronic LSD treatment, LSD-stimulated [35S]GTPgammaS binding, an index of G-protein coupling, was measured in the rat brain by autoradiography. After chronic LSD, a significant reduction in LSD-stimulated [35S]GTPgammaS binding was observed in the medial prefrontal cortex and anterior cingulate cortex. Furthermore, chronic LSD produced a significant reduction in 2,5-dimethoxy-4-iodoamphetamine-stimulated [35S]GTPgammaS binding in medial prefrontal cortex and anterior cingulate cortex, which was blocked by MDL 100907, a selective 5-HT2A receptor antagonist, but not SB206553, a 5-HT2C receptor antagonist, indicating a reduction in 5-HT2A receptor signaling. 125I-LSD binding to 5-HT2A receptors was reduced in cortical regions, demonstrating a reduction in 5-HT2A receptor density. Taken together, these results indicate that adaptive changes in LSD-stimulated serotonin receptor signaling may mediate tolerance to the discriminative stimulus effects of LSD.
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Affiliation(s)
- Paul J Gresch
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
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25
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Benneyworth MA, Smith RL, Barrett RJ, Sanders-Bush E. Complex discriminative stimulus properties of (+)lysergic acid diethylamide (LSD) in C57Bl/6J mice. Psychopharmacology (Berl) 2005; 179:854-62. [PMID: 15645221 DOI: 10.1007/s00213-004-2108-z] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/30/2004] [Accepted: 11/04/2004] [Indexed: 10/25/2022]
Abstract
RATIONALE The drug discrimination procedure is the most frequently used in vivo model of hallucinogen activity. Historically, most drug discrimination studies have been conducted in the rat. With the development of genetically modified mice, a powerful new tool has become available for investigating the mechanisms of drug-induced behavior. The current paper is part of an ongoing effort to determine the utility of the drug discrimination technique for evaluating hallucinogenic drugs in mice. OBJECTIVE To establish the training procedures and characterize the stimulus properties of (+)lysergic acid diethylamide (LSD) in mice. METHODS Using a two-lever drug discrimination procedure, C57Bl/6J mice were trained to discriminate 0.45 mg/kg LSD vs saline on a VI30 sec schedule of reinforcement, with vanilla-flavored Ensure serving as the reinforcer. RESULTS As in rats, acquisition was orderly, but the training dose was nearly five-fold higher for mice than rats. LSD lever selection was dose-dependent. Time-course studies revealed a rapid loss of the LSD stimulus effects. The 5-HT(2A/2C) receptor agonist, 2,5-dimethoxy-4-bromoamphetamine [(-)DOB] (1.0 mg/kg), substituted fully for LSD and the 5-HT(1A) receptor agonist, 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) (1.6 mg/kg), substituted partially for LSD. Pretreatment with the 5-HT(2A) receptor-selective antagonist, MDL 100907, or the 5-HT(1A)-selective antagonist WAY 100635, showed that each antagonist only partially blocked LSD discrimination. Substitution of 1.0 mg/kg (-)DOB for LSD was fully blocked by pretreatment with MDL 100907 but unaltered by WAY 100635 pretreatment. CONCLUSIONS These data suggest that in mice the stimulus effects of LSD have both a 5-HT(2A) receptor and a 5-HT(1A) receptor component.
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Affiliation(s)
- Michael A Benneyworth
- Department of Pharmacology, Vanderbilt University School of Medicine, 8148 MRB III, Nashville, TN 37232, USA
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26
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Arnt J, Bøgesø KP, Boeck V, Christensen AV, Dragsted N, Hyttel J, Skarsfeldt T. In vivo pharmacology of irindalone, a 5-HT2receptor antagonist with predominant peripheral effects. Drug Dev Res 2004. [DOI: 10.1002/ddr.430160107] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Abstract
Hallucinogens (psychedelics) are psychoactive substances that powerfully alter perception, mood, and a host of cognitive processes. They are considered physiologically safe and do not produce dependence or addiction. Their origin predates written history, and they were employed by early cultures in a variety of sociocultural and ritual contexts. In the 1950s, after the virtually contemporaneous discovery of both serotonin (5-HT) and lysergic acid diethylamide (LSD-25), early brain research focused intensely on the possibility that LSD or other hallucinogens had a serotonergic basis of action and reinforced the idea that 5-HT was an important neurotransmitter in brain. These ideas were eventually proven, and today it is believed that hallucinogens stimulate 5-HT(2A) receptors, especially those expressed on neocortical pyramidal cells. Activation of 5-HT(2A) receptors also leads to increased cortical glutamate levels presumably by a presynaptic receptor-mediated release from thalamic afferents. These findings have led to comparisons of the effects of classical hallucinogens with certain aspects of acute psychosis and to a focus on thalamocortical interactions as key to understanding both the action of these substances and the neuroanatomical sites involved in altered states of consciousness (ASC). In vivo brain imaging in humans using [(18)F]fluorodeoxyglucose has shown that hallucinogens increase prefrontal cortical metabolism, and correlations have been developed between activity in specific brain areas and psychological elements of the ASC produced by hallucinogens. The 5-HT(2A) receptor clearly plays an essential role in cognitive processing, including working memory, and ligands for this receptor may be extremely useful tools for future cognitive neuroscience research. In addition, it appears entirely possible that utility may still emerge for the use of hallucinogens in treating alcoholism, substance abuse, and certain psychiatric disorders.
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Affiliation(s)
- David E Nichols
- Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmacal Sciences, Purdue University, West Lafayette, IN 47907-2091, USA.
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28
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Appel JB, West WB, Buggy J. LSD, 5-HT (serotonin), and the evolution of a behavioral assay. Neurosci Biobehav Rev 2004; 27:693-701. [PMID: 15019419 DOI: 10.1016/j.neubiorev.2003.11.012] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Research in our laboratory, supported by NIDA and facilitated by Roger Brown, has indicated that serotonergic neuronal systems are involved in the discriminative stimulus effects of LSD. However, the only compounds that fully antagonize the LSD cue act at both serotonin (5-HT) and dopamine (DA) receptors. In addition, substitution for LSD in standard drug vs. no-drug (DND) discriminations does not necessarily predict either similar mechanisms of action or hallucinogenic potency because 'false positives' occur when animals are given drugs such as lisuride (LHM), quipazine, or, possibly, yohimbine. These effects can be greatly reduced by using drug vs. drug (D-D), drug vs. drug vs. no drug (D-ND), or drug vs. ' other' drug (saline, cocaine, pentobarbital) training procedures. Additional studies, in which drugs were administered directly into the cerebral ventricles or specific brain areas, suggest that structures containing terminal fields of serotonergic neurons might be involved in the stimulus effects of LSD.
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Affiliation(s)
- James B Appel
- Department of Psychology, University of South Carolina, 1512 Pendleton Street, Columbia, SC 29208, USA.
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Gatch MB. Discriminative stimulus effects of m-chlorophenylpiperazine as a model of the role of serotonin receptors in anxiety. Life Sci 2003; 73:1347-67. [PMID: 12850497 DOI: 10.1016/s0024-3205(03)00422-3] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Serotonin is known to play a role in anxiety. The roles of serotonin reuptake and 5-HT1A receptors have been well characterized, but the contribution of other serotonin receptor subtypes is not as clear. 1-(3-Chlorophenyl)-piperazine (mCPP), which binds non-selectively to a wide range of serotonin receptors, has often been used to produce anxiety in humans and in animal models. Because functional assays indicate that mCPP is significantly more potent at 5-HT2C receptors, it may serve as a tool to investigate the contribution of 5-HT2C receptors to anxiety. This paper reviews the results of behavioral tests using mCPP, including the drug discrimination assay, to model anxiety. Although the discriminative stimulus effects of mCPP do not seem to be a useful screen for general anxiolytics, they do seem to be useful for characterization of the contribution of 5-HT1B and 5-HT2C receptors to the mediation of anxiety-like behaviors.
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Affiliation(s)
- Michael B Gatch
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, 3500 Camp Bowie Blvd., Fort Worth, TX 76107-2699, USA.
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McCreary AC, Filip M, Cunningham KA. Discriminative stimulus properties of (+/-)-fenfluramine: the role of 5-HT2 receptor subtypes. Behav Neurosci 2003; 117:212-21. [PMID: 12708517 DOI: 10.1037/0735-7044.117.2.212] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The role of serotonin 5-HT2 receptors (5-HT2R) in the discriminative stimulus effects of fenfluramine was investigated. Male Sprague-Dawley rats were trained to discriminate (+/-)-fenfluramine (2 mg/kg ip) from saline using a 2-lever, water-reinforced paradigm. Drug-lever responding after fenfluramine was dose-dependent. The 5-HT(2C/1B)R agonist mCPP and the 5-HT(2C)R agonist MK 212 fully substituted, whereas the 5-HT(2A/2C)R agonist DOI partially substituted, for the training drug. The 5-HT(2B)R agonist BW 723C86 engendered saline-lever responding. The 5-HT(2C/2B)R antagonist SB 206553 completely antagonized the fenfluramine discrimination a well as the full substitutions of mCPP and MK 212 and the partial substitution of DOI. The selective 5-HT(2A)R antagonist M100907 partially suppressed the stimulus effects of fenfluramine, mCPP, and MK 212 and almost fully attenuated the partial substitution of DOI. RS 102221, a selective 5-HT(2C)R antagonist that does not cross the blood-brain barrier, did not alter the fenfluramine cue. Results demonstrate that the discriminative stimulus effects of fenfluramine are centrally mediated by 5-HT(2C)R and to some extent by 5-HT(2A)R.
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Affiliation(s)
- Andrew C McCreary
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston 77555, USA
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Frankel PS, Cunningham KA. The hallucinogen d-lysergic acid diethylamide (d-LSD) induces the immediate-early gene c-Fos in rat forebrain. Brain Res 2002; 958:251-60. [PMID: 12470860 DOI: 10.1016/s0006-8993(02)03548-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The hallucinogen d-lysergic acid diethylamide (d-LSD) evokes dramatic somatic and psychological effects. In order to analyze the neural activation induced by this unique psychoactive drug, we tested the hypothesis that expression of the immediate-early gene product c-Fos is induced in specific regions of the rat forebrain by a relatively low, behaviorally active, dose of d-LSD (0.16 mg/kg, i.p.); c-Fos protein expression was assessed at 30 min, and 1, 2 and 4 h following d-LSD injection. A time- and region-dependent expression of c-Fos was observed with a significant increase (P<0.05) in the number of c-Fos-positive cells detected in the anterior cingulate cortex at 1 h, the shell of the nucleus accumbens at 1 and 2 h, the bed nucleus of stria terminalis lateral at 2 h and the paraventricular hypothalamic nucleus at 1, 2 and 4 h following systemic d-LSD administration. These data demonstrate a unique pattern of c-Fos expression in the rat forebrain following a relatively low dose of d-LSD and suggest that activation of these forebrain regions contributes to the unique behavioral effects of d-LSD.
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Affiliation(s)
- Paul S Frankel
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, 301 University Blvd, Galveston, TX 77555-1031, USA.
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Davidson C, Lazarus C, Xiong X, Lee TH, Ellinwood EH. 5-HT2 receptor antagonists given in the acute withdrawal from daily cocaine injections can reverse established sensitization. Eur J Pharmacol 2002; 453:255-63. [PMID: 12398913 DOI: 10.1016/s0014-2999(02)02390-7] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Male Sprague-Dawley rats were given two separate sensitizing regimens of cocaine (7 days on, 7 days off, 7 days on at 40 mg/kg/day, s.c.) or saline injections. Half of the animals also received a drug with 5-hydroxytryptamine-2 (5-HT2) receptor antagonist properties (clozapine, 3 mg/kg; mianserin 6 mg/kg; ketanserin 1 mg/kg, all s.c.) or saline during the second cocaine dosing regimen in the acute withdrawal period, 3.5 h after each cocaine injection. On day 10 of withdrawal animals were challenged with cocaine (7.5 mg/kg, i.p.) and assessed by a behavioral rating scale and locomotor activity monitoring. The 5-HT2 receptor antagonists, but not saline, reversed behavioral sensitization and had little effect on behavior in the control animals. 5-HT2 receptor antagonists, therefore, may be a useful treatment for cocaine addicts that have undergone previous sensitization periods. The pharmacological profile of these antagonists suggests that the 5-HT2A receptor subtype may mediate this effect.
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Affiliation(s)
- Colin Davidson
- Department of Psychiatry, Box 3870, Duke University Medical Center, Durham, NC 27710, USA
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Romano AG, Hood H, Harvey JA. Dissociable effects of the 5-HT(2) antagonist mianserin on associative learning and performance in the rabbit. Pharmacol Biochem Behav 2000; 67:103-10. [PMID: 11113489 DOI: 10.1016/s0091-3057(00)00298-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Serotonin 5-HT(2) antagonists that significantly retard the acquisition of classically conditioned responses (CRs) also impair the performance of the unconditioned response (UR). Effects on the UR appear to be due to an inverse agonist action at the 5-HT(2) receptor. These findings raised the possibility that the learning deficits were either secondary to a performance deficit and/or that the retardation of learning was not due to actions at the serotonin 5-HT(2) receptor. In this study, we examined the effects of the 5-HT(2)-receptor antagonists, namely mianserin and D-2-bromolysergic acid diethylamide hydrogen tartrate (BOL), on CR acquisition. We also determined whether the retarded acquisition of CRs produced by mianserin (a) was due to an action at the 5-HT(2) receptor and (b) was secondary to a performance deficit. Effects of drugs on CR acquisition, maintenance, and retention were determined during trace-conditioning of the rabbit's nictitating membrane (NM) response. BOL (0.058 to 5.8 micromol/kg) had no effect on CR acquisition, whereas mianserin (0.1 to 10 micromol/kg) produced a significant and dose-dependent retardation of CR acquisition. The retarded CR acquisition produced by mianserin (10 micromol/kg) was due to its actions at the 5-HT(2) receptor, because this effect was completely blocked by a dose of BOL (5.8 micromol/kg) that had no effect when given alone. Neither maintenance nor retention of learning was affected by mianserin treatment during acquisition. We conclude that mianserin acts as an inverse agonist at the serotonin 5-HT(2) receptor to produce both a retardation of CR acquisition and an impairment of the UR. However, the learning and performance effects of mianserin are separable.
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Affiliation(s)
- A G Romano
- Department of Pharmacology, MCP Hahnemann University, 3200 Henry Avenue, Philadelphia, PA 19129, USA.
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Appel JB, West WB, Rolandi WG, Alici T, Pechersky K. Increasing the selectivity of drug discrimination procedures. Pharmacol Biochem Behav 1999; 64:353-8. [PMID: 10515312 DOI: 10.1016/s0091-3057(99)00089-1] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In an attempt to increase the selectivity of drug discrimination, rats were trained to discriminate LSD (0.08 mg/kg) from a group of "other" compounds consisting of cocaine (10 mg/kg), pentobarbital (5 mg/kg), and saline. Acquisition of this LSD-other discrimination was rapid (31 days) in chambers equipped with retractable levers and did not differ significantly from that of a group of animals trained to discriminate LSD from saline (26 days). In substitution (generalization) tests, hallucinogens such as LSD, DMT, and DOM mimicked LSD in a dose-dependent manner in both groups. The designer drug (+/-)MDMA substituted for LSD in the LSD-other group (ED50 = 1.38) but did not substitute for the training drug in the LSD-ND group; neither (+) MDMA nor PCP mimicked LSD in either group. Most importantly, lisuride, quipazine, and yohimbine, drugs that have been described as "false positives," substituted for LSD in animals trained to discriminate LSD from saline (ED50s = 0.012, 1.662, 2.344, respectively), but not in animals trained to discriminate LSD from other drugs. Thus, the LSD-other training procedure can be described as more selective than the standard drug-ND procedure.
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Affiliation(s)
- J B Appel
- Behavioral Pharmacology Laboratory, Department of Psychology, University of South Carolina, Columbia 29208, USA
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Abstract
1. Rats were trained to discriminate i.p. injections of a 5-HT agonist, LSD (0.08 mg/kg, n = 12) or a DA agonist, cocaine (10 mg/kg; n = 16) in a two lever, drug discrimination situation. 2. Animals were tested with fluoxetine (0.625-10 mg/kg) alone and in combination with low doses of the training drugs. 3. Fluoxetine did not substitute for either LSD or cocaine at any dose tested. A relatively low dose of fluoxetine (2.5 mg/kg) potentiated the discriminability of cocaine (2.5 mg/kg) from saline. A higher dose of fluoxetine (5.0 mg/kg) significantly enhanced the effects of a low dose of LSD (0.02 mg/kg), but only to 41.7% responses on the LSD-appropriate lever. 4. The data suggest that fluoxetine alters the discriminative stimulus properties of cocaine to a greater extent than those of LSD. 5. The ability of fluoxetine to potentiate the cocaine cue (but not to substitute for cocaine) suggests that both of those drugs affect DA systems, but do so through different mechanisms. For example, fluoxetine may not inhibit DA reuptake (to the same extent as cocaine), but may have other dopaminergic actions such as increasing DA receptor density.
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Affiliation(s)
- B Simon
- Department of Psychology, University of South Carolina, Columbia, USA
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Monte AP, Marona-Lewicka D, Parker MA, Wainscott DB, Nelson DL, Nichols DE. Dihydrobenzofuran analogues of hallucinogens. 3. Models of 4-substituted (2,5-dimethoxyphenyl)alkylamine derivatives with rigidified methoxy groups. J Med Chem 1996; 39:2953-61. [PMID: 8709129 DOI: 10.1021/jm960199j] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Tetrahydrobenzodifuran functionalities were employed as conformationally restricted bioisosteres of the aromatic methoxy groups in prototypical hallucinogenic phenylalkylamines 1 and 2. Thus, a series of 8-substituted 1-(2,3,6,7-tetrahydrobenzo[1,2-b:4,5-b']difuran-4-yl)-2-aminoal kanes (7a-e) were prepared and evaluated for activity in the two-lever drug discrimination paradigm in rats trained to discriminate saline from LSD tartrate (0.08 mg/kg) and for the ability to displace [3H]ketanserin from rat cortical homogenate 5-HT2A receptors and [3H]-8-OH-DPAT from rat hippocampal homogenate 5-HT1A receptors. In addition, 1-(8-bromo-2,3,6,7-tetrahydrobenzo[1,2-b:4,5-b']difuran-4-yl)-2-am inopropane (7b), which was found to be extremely potent in the rat in vivo assays, was evaluated for its ability to compete with [125I]DOI and [3H]ketanserin binding to cells expressing cloned human 5-HT2A, 5-HT2B, and 5-HT2C receptors. All of the dihydrofuranyl compounds having a hydrophobic substituent para to the alkylamine side chain had activities in both the in vitro and in vivo assays that equaled or surpassed the activity of the analogous conformationally flexible parent compounds. For example, 7b substituted for LSD in the drug discrimination assay with an ED50 of 61 nmol/kg and had Kj values in the nanomolar to subnanomolar range for the displacement of radioligand from rat and human 5-HT2 receptors, making it one of the most potent hallucinogen-like phenylalkylamine derivatives reported to date. The results suggest that the dihydrofuran rings in these new analogues effectively model the active binding conformations of the methoxy groups of the parent compounds 1 and 2. In addition, the results provide information about the topography and relative orientation of residues involved in agonist binding in the serotonin 5-HT2 receptors.
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Affiliation(s)
- A P Monte
- Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmacal Sciences, Purdue University, West Lafayette, Indiana 47907, USA
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Fiorella D, Rabin RA, Winter JC. The role of the 5-HT2A and 5-HT2C receptors in the stimulus effects of hallucinogenic drugs. I: Antagonist correlation analysis. Psychopharmacology (Berl) 1995; 121:347-56. [PMID: 8584617 DOI: 10.1007/bf02246074] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Investigations conducted over the past 3 decades have demonstrated that serotonergic receptors, specifically the 5-HT2A and 5-HT2C subtypes, play an important role in the behavioral effects of hallucinogenic compounds. The present study was designed to determine the respective significance of these two receptors in the stimulus effects of LSD and (-)DOM in the rat. Specifically, the interactions of a series of serotonergic antagonists (risperidone, pirenpirone, metergoline, ketanserin, loxapine, LY53857, pizotyline, spiperone, cyprohepatadine, mesulergine, promethazine, and thioridazine) with the LSD stimulus and the (-)DOM stimulus in LSD-trained subjects was defined. From these data, IC50 values were determined for the inhibition of the LSD-appropriate responding elicited by either 0.1 mg/kg LSD (15-min pretreatment time) or 0.4 mg/kg (-)DOM (75-min pretreatment). In addition, the affinities of these antagonists for 5-HT2A and 5-HT2C receptors were determined in radioligand competition studies, 5-HT2A affinity correlated significantly with IC50 values for the blockade of the LSD (r = +0.75, P < 0.05) and (-)DOM (r = +0.95, P < 0.001) stimuli in the LSD trained subjects. 5-HT2C affinity did not correlate significantly with either series of IC50 values. These data indicate that (1) the stimulus effects of LSD, and (2) the substitution of (-)DOM for the LSD stimulus are mediated by agonist activity at 5-HT2A receptors.
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Affiliation(s)
- D Fiorella
- Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, USA
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Fiorella D, Rabin RA, Winter JC. Role of 5-HT2A and 5-HT2C receptors in the stimulus effects of hallucinogenic drugs. II: Reassessment of LSD false positives. Psychopharmacology (Berl) 1995; 121:357-63. [PMID: 8584618 DOI: 10.1007/bf02246075] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
In the context of animal studies of hallucinogens, an LSD-false positive is defined as a drug known to be devoid of hallucinogenic activity in humans but which nonetheless fully mimics LSD in animals. Quipazine, MK-212, lisuride, and yohimbine have all been reported to be LSD false positives. The present study was designed to determine whether these compounds also substitute for the stimulus effects of the more pharmacologically selective hallucinogen (-)DOM (0.56 mg/kg, 75-min pretreatment time). The LSD and (-)DOM stimuli fully generalized to quipazine (3.0 mg/kg) and lisuride (0.2 mg/kg), but only partially generalized to MK-212 (0.1-1.0 mg/kg) and yohimbine (2-20 mg/kg). In combination tests, pirenpirone (0.08 mg/kg), a compound with both D2 and 5-HT2A affinity, blocked the substitution of quipazine and lisuride for the (-)DOM stimulus. Ketanserin (2.5 mg/kg), an antagonist with greater than 1 order of magnitude higher affinity for 5-HT2A receptors than either 5-HT2C or D2 receptors, also fully blocked the substitution of these compounds for the (-)DOM stimulus, while the selective D2 antagonist thiothixene (0.1-1.0 mg/kg) failed to block the substitution of lisuride for the (-)DOM stimulus. These results suggest that quipazine and lisuride substitute for the stimulus properties of the phenylalkglamine hallucinogen (-)DOM via agonist activity at 5-HT2A receptors. In addition, these results suggest that 5-HT2A agonist activity may be required, but is not in itself sufficient, for indolamine and phenylalkglamine compounds to elicit hallucinations in humans. Finally, it is concluded that MK-212 and yohimbine are neither LSD nor (-)DOM false positives.
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Affiliation(s)
- D Fiorella
- Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, State University of New York at Buffalo, USA
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Marona-Lewicka D, Nichols DE. Complex stimulus properties of LSD: a drug discrimination study with alpha 2-adrenoceptor agonists and antagonists. Psychopharmacology (Berl) 1995; 120:384-91. [PMID: 8539318 DOI: 10.1007/bf02245809] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The influence of several alpha 2-adrenergic agents on the discriminative stimulus (DS) properties of lysergic acid diethylamide (LSD) was studied in rats trained to discriminate 0.08 mg/kg (186 nmol/kg) of LSD from saline in a two-lever operant paradigm. Only yohimbine fully mimicked LSD with an ED50 of 2.05 mg/kg (5.24 mumol/kg). Yohimbine's 5-HT1A agonist properties may be responsible for this substitution. Other alpha 2-adrenoceptor antagonists, idazoxan with an agonist/antagonist profile at 5-HT1A receptors and RS 26026-197, a highly selective alpha 2-adrenoceptor antagonist, failed to produce substitution. Clonidine, an alpha 2-adrenoceptor agonist, did not substitute for LSD but the response rate was dose-dependently reduced. None of the alpha 2-adrenergic agents used for pretreatment before LSD inhibited the response to the LSD training dose. Coadministration of clonidine with LSD produced a leftward shift of the dose-response relationship of LSD without a significant change in the slope of the dose-response line. Simultaneous administration of alpha 2-adrenergic agents with LSD shifted the dose-response curve to the left only when the adrenergic agent also possessed at least moderate affinity for the 5-HT1A receptor. In addition, radioligand competition experiments were performed that showed LSD to have relatively high affinity (Ki = 37 nM) for [3H]clonidine-labeled sites in rat cortex with lower affinity for [3H]yohimbine labeled sites. While previous studies have suggested that the nature of the LSD cue may be essentially expressed by 5-HT2 receptor activation, the present data show that this cue can be modulated by effects of LSD at 5-HT1A and at other monoamine neurotransmitter receptors.
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Affiliation(s)
- D Marona-Lewicka
- Department of Pharmacology and Toxicology, School of Pharmacy and Pharmacal Sciences, Purdue University, West Lafayette, IN 47907, USA
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40
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Fiorella D, Palumbo PA, Rabin RA, Winter JC. The time-dependent stimulus effects of R(-)-2,5-dimethoxy-4-methamphetamine (DOM): implications for drug-induced stimulus control as a method for the study of hallucinogenic agents. Psychopharmacology (Berl) 1995; 119:239-45. [PMID: 7659772 DOI: 10.1007/bf02246166] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The pharmacodynamic characteristics of the stimulus effects of the hallucinogens d-LSD and (-)DOM were investigated in the rat. The stimulus control induced by (-)DOM (0.56 mg/kg) was significantly less stable at the 15-min pretreatment time than at the 75-min pretreatment time. In addition, (-)DOM (0.8 mg/kg) produced a time-dependent substitution for the LSD stimulus in LSD trained subjects (0.1 mg/kg, 15-min pretreatment time). As pretreatment times were increased, the substitution of (-)DOM (0.8 mg/kg) for the LSD stimulus increased, culminating in a maximal level of 99.5% LSD-appropriate responding at the 75-min pre-treatment time. A dose-response relationship for the substitution of (-)DOM (75-min pretreatment time) for the LSD stimulus, indicated that 0.2 mg/kg (-)DOM was the minimum dose which elicited greater than 90% LSD-appropriate responding. LSD (0.32 mg/kg, 15-min pretreatment time) fully substituted for (-)DOM in the (-)DOM trained subjects (0.56 mg/kg, 75-min pretreatment time). These findings suggest that the pharmacodynamic parameters of d-LSD and (-)DOM-induced stimulus control differ. The time of onset for the stimulus effects of (-)DOM is markedly longer than that of LSD in the rat.
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Affiliation(s)
- D Fiorella
- Department of Pharmacology and Toxicology, School of Medicine and Biomedical Sciences, State University of New York at Buffalo 14214, USA
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41
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Recent Developments in the Chemistry of Pyrido[1,2-a]pyrimidines. ADVANCES IN HETEROCYCLIC CHEMISTRY 1995. [DOI: 10.1016/s0065-2725(08)60473-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Huang X, Marona-Lewicka D, Pfaff RC, Nichols DE. Drug discrimination and receptor binding studies of N-isopropyl lysergamide derivatives. Pharmacol Biochem Behav 1994; 47:667-73. [PMID: 8208787 DOI: 10.1016/0091-3057(94)90172-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Isopropyl (IPLA), N-methyl-N-isopropyl (MIPLA), N-ethyl-N-isopropyl (EIPLA), and N,N-diisopropyl (DIPLA) lysergamides were evaluated for lysergic acid diethylamide (LSD)-like activity. In rats trained to discriminate 0.08 mg/kg LSD tartrate from saline, each of the subject compounds completely substituted, with an ED50 two to three times larger than that of LSD except for DIPLA, which had an ED50 about eightfold greater. Similarly, all the compounds displaced [125I](R)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane ([125I]DOI) from rat cortical homogenates and displaced [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([3H]8-OH-DPAT) from rat hippocampal homogenates with KI values similar to those of LSD, again with the exception of DIPLA, which had about nine- and fourfold lower affinities, respectively. Interestingly, all the compounds had four- to fivefold lower affinities than LSD in displacing [3H]ketanserin from 5-HT2 binding sites. Molecular modeling studies found that all the compounds had low energy conformations similar to LSD. No correlation between the activity of the compounds and the preferred conformation of the amide substituents was apparent. In summary, N-alkyl-N-isopropyl analogs of LSD retain LSD-like activity in drug discrimination and 5-HT1A and 5-HT2 agonist binding assays only until the N-alkyl substitution is as large as ethyl; LSD-like activity dramatically drops when the second alkyl substituent is N-isopropyl.
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Affiliation(s)
- X Huang
- Department of Medicinal Chemistry and Pharmacognosy, School of Pharmacy and Pharmacal Sciences, Purdue University, West Lafayette, IN 47907
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Holtzman SG, Steinfels GF. Monoamine systems in the discriminative effects of spiradoline, a kappa-opioid agonist. Pharmacol Biochem Behav 1994; 47:575-8. [PMID: 8208776 DOI: 10.1016/0091-3057(94)90161-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The results of studies on mice indicate that the antinociceptive effects of kappa-opioid agonists are due, in part, to activation of the 5-HT2 type of serotonin receptor. One objective of this study was to determine if the discriminative effects of spiradoline, a kappa-opioid agonist, are mediated by 5-HT2 receptors in rats also. A second objective was to confirm findings that dopamine receptor antagonists produce spiradoline-like discriminative effects (Ohno et al., 1992). Rats were trained to discriminate between spiradoline (3.0 mg/kg) and saline in a discrete-trial avoidance/escape procedure. In subsequent tests of stimulus generalization, the discriminative effects of spiradoline were not mimicked by fenfluramine (0.3-10 mg/kg) or fluoxetine (1.0-10 mg/kg), drugs that enhance serotonergically mediated neurotransmission, nor were they blocked by the 5-HT2 antagonists pirenperone (0.01-1.0 mg/kg) and ketanserin (0.1-10 mg/kg), or potentiated by fluoxetine pretreatment. Neither the dopamine receptor antagonists haloperidol (0.01-0.3 mg/kg) and sulpiride (3.0-100 mg/kg) nor the agonists apomorphine (0.03-0.3 mg/kg) and d-amphetamine (0.1-3.0 mg/kg) engendered spiradoline-like discriminative effects. These results demonstrate further the pharmacological specificity of the discriminative effects of spiradoline, but provide no evidence for mediation by serotonergic or dopaminergic systems.
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Affiliation(s)
- S G Holtzman
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322-3090
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44
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Lacosta S, Roberts DC. MDL 72222, ketanserin, and methysergide pretreatments fail to alter breaking points on a progressive ratio schedule reinforced by intravenous cocaine. Pharmacol Biochem Behav 1993; 44:161-5. [PMID: 8430119 DOI: 10.1016/0091-3057(93)90295-5] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The effects of three serotonin [5-hydroxytryptamine (5-HT)] receptor antagonists on cocaine self-administration behavior were investigated. Specifically, the effects of MDL 72222 (a specific 5-HT3 receptor antagonist), ketanserin (a specific 5HT2 receptor antagonist), and methysergide (an aselective 5-HT1/5-HT2 receptor antagonist) on the breaking points reached by rats on a progressive ratio schedule for cocaine reinforcement were examined. Pretreatments with MDL 72222 (7.5-1,920 micrograms/kg, SC), ketanserin (0.4-6.4 mg/kg, IP), and methysergide (2.5-20 mg/kg, IP) failed to alter breaking points from baseline values. Although tested at twice the highest doses previously reported to have significant behavioral effects, the three 5-HT receptor antagonists were without effect. These data suggest that relatively specific blockade of 5-HT receptor subtypes does not influence the reinforcing effects of cocaine.
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Affiliation(s)
- S Lacosta
- Department of Psychology, Carleton University, Ottawa, Canada
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45
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Koek W, Jackson A, Colpaert FC. Behavioral pharmacology of antagonists at 5-HT2/5-HT1C receptors. Neurosci Biobehav Rev 1992; 16:95-105. [PMID: 1553110 DOI: 10.1016/s0149-7634(05)80056-9] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The possible implication of 5-HT2 receptors in CNS disorders such as schizophrenia, anxiety and depression suggests that 5-HT2 antagonists may be useful in the treatment of these disorders. The present review examines behavioral procedures used to characterize 5-HT2 antagonist properties of compounds and behavioral models of clinical activity in which 5-HT2 antagonists have been reported to be active. The pharmacological profile of 5-HT2 receptors in part resembles that of 5-HT1C receptors. Responses that have been proposed to involve the activation of 5-HT1C receptors are examined for their usefulness to detect 5-HT1C antagonist properties of compounds; these responses would help to differentiate 5-HT2 from 5-HT1C antagonist activity.
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Affiliation(s)
- W Koek
- Neurobiology Division, FONDAX-Groupe de Recherche SERVIER, Puteaux, France
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46
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Cunningham KA, Callahan PM. Monoamine reuptake inhibitors enhance the discriminative state induced by cocaine in the rat. Psychopharmacology (Berl) 1991; 104:177-80. [PMID: 1831559 DOI: 10.1007/bf02244175] [Citation(s) in RCA: 119] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Cocaine inhibits the reuptake of dopamine (DA), norepinephrine (NE), and serotonin (5-HT). To investigate the relative role of such reuptake processes in the discriminative stimulus properties of cocaine, male rats (N = 16) were trained to discriminate cocaine (10 mg/kg) from saline in a two-lever, water-reinforced drug discrimination task and were administered neuroactive compounds during substitution or combination tests. The DA reuptake inhibitor GBR 12909 (2-16 mg/kg) completely mimicked cocaine. The reuptake inhibitors for NE (desipramine; 2-8 mg/kg) and 5-HT (fluoxetine; 0.625-5 mg/kg) did not substitute for the training drug. A low dose of either desipramine (3 mg/kg), fluoxetine (1.25 mg/kg), or GBR 12909 (2 mg/kg) coadministered with low doses of cocaine (0.625-2.5 mg/kg) enhanced the discriminative stimulus properties of this psychostimulant. The dose predicted to elicit 50% drug-lever responding is reduced (ED50) in the presence of desipramine (0.38 mg/kg), fluoxetine (0.79 mg/kg) or GBR 12909 (0.84 mg/kg) compared to the ED50 for cocaine (1.57 mg/kg) in the absence of any reuptake inhibitor. The finding that GBR 12909 mimics the cocaine cue corroborates the hypothesis that the stimulus properties of cocaine are mediated predominantly by DA systems. The potentiation of the stimulus effects of cocaine by monoamine reuptake inhibitors in rats suggests that these drugs could also amplify the subjective effects of cocaine in humans, a possibility that should be considered given the current use of antidepressants in the treatment of cocaine abusers.
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Affiliation(s)
- K A Cunningham
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston 77550
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47
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Callahan PM, Appel JB, Cunningham KA. Dopamine D1 and D2 mediation of the discriminative stimulus properties of d-amphetamine and cocaine. Psychopharmacology (Berl) 1991; 103:50-5. [PMID: 2006243 DOI: 10.1007/bf02244073] [Citation(s) in RCA: 114] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Evidence suggests that stimulants such as d-amphetamine and cocaine act presynaptically by increasing the amount of dopamine (DA) available to stimulate postsynaptic DA receptors. Since two subpopulations of DA receptors (D1 and D2) exist, we investigated the role of both of these receptor subtypes in mediating the internal "state" produced by these stimulants. Two groups of rats (N = 8/group) were trained to discriminate intraperitoneal (IP) injections of either d-amphetamine (1 mg/kg) or cocaine (10 mg/kg) from saline in a two-lever, water-reinforced, drug discrimination task. After stable performance was established (i.e., more than 85% correct under each training condition), substitution and combination tests were conducted with selective D1 and D2 agonists and antagonists. The D2 agonist quinpirole (0.0313-0.125 mg/kg) mimicked both stimulant cues while the D1 agonist SKF 38393 (5-20 mg/kg) substituted partially for cocaine but not d-amphetamine. Combination tests with DA antagonists indicated that both the D1 antagonist SCH 23390 (0.0063-0.25 mg/kg) and the D2 antagonist haloperidol (0.125-0.5 mg/kg) attenuated the effects of both stimulants; in addition, the substitution of cocaine (20 mg/kg) for d-amphetamine was blocked by both DA antagonists. The ability of both D1 and D2 antagonists to attenuate the stimulus effects of d-amphetamine and cocaine raises the possibility that a synergistic ("enabling") interaction between D1 and D2 receptors may modulate stimulant cues.
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Affiliation(s)
- P M Callahan
- Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston 77550
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48
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Callahan PM, Appel JB. Differentiation between the stimulus effects of (+)-lysergic acid diethylamide and lisuride using a three-choice, drug discrimination procedure. Psychopharmacology (Berl) 1990; 100:13-8. [PMID: 2296621 DOI: 10.1007/bf02245782] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The discriminative stimulus properties of (+)-lysergic acid diethylamide (LSD) and lisuride hydrogen maleate (LHM), were compared in a three-choice, water reinforced (FR 20) situation in which rats were required to press one lever following LSD (0.08 mg/kg), a second lever following LHM (0.04 mg/kg), and a third lever following saline. Reliable drug-appropriate responding was established in 72 sessions. Dose-response tests with LSD and LHM indicated that, as dose increased, the per cent of responding on the lever associated with the particular training drug also increased; little or no cross-transfer occurred between LSD and LHM. In generalization tests, the serotonin (5-HT) agonist quipazine substituted for LSD but not LHM while the dopamine (DA) agonist apomorphine mimicked LHM but not LSD; an unrelated compound, pentylenetetrazol (PTZ), produced responding on the saline-appropriate lever. In combination tests, 5-HT antagonists (e.g., BC-105 and low doses of pirenperone) blocked responding on the LSD lever while DA antagonists (e.g., haloperidol and much higher doses of pirenperone) blocked LHM-appropriate responding. These data suggest that the three-lever (D-D-N) procedure is similar to, but can be more sensitive than the two-lever (D-N) procedure (because it can differentiate between LSD and LHM); they therefore at least partially support the hypothesis that three-choice discriminations can be conceptualized as two separate, two-choice (D-N) discriminations (Jarbe and Swedberg 1982). The results also confirm suggestion that the stimulus effects of LSD and LHM are mediated by different mechanisms; the primary action of LSD is serotonergic (5-HT2), while that of LHM is dopaminergic (White 1986).
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Affiliation(s)
- P M Callahan
- Department of Psychology, University of South Carolina, Columbia 29208
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Wing LL, Tapson GS, Geyer MA. 5HT-2 mediation of acute behavioral effects of hallucinogens in rats. Psychopharmacology (Berl) 1990; 100:417-25. [PMID: 2138338 DOI: 10.1007/bf02244617] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
In rats tested during their first exposure to a Behavioral Pattern Monitor chamber, acute injections of the 5HT-2 agonists mescaline, quipazine, 2,5-dimethoxy-4-iodoamphetamine (DOI), 2,5-dimethoxy-4-methylamphetamine (DOM), or 2,5-dimethoxy-4-ethylamphetamine (DOET) produced an inhibition of locomotor and investigatory behavior during the first 30 min of the test session. This suppression of exploratory behavior was attenuated when rats were familiarized with the testing chamber prior to the administration of DOI. Hence, as previously observed with both LSD and DOM, 5HT-2 agonists appear to potentiate the normal neophobic reaction to a novel environment. The mixed 5HT-1 and 5HT-2 agonist 5-methoxy-N,N-dimethyltryptamine (5MeODMT) also produced a decrease in activity when animals were tested in the novel environment. However, as previously found with 5HT-1A agonists, this effect was unchanged when animals were tested in the familiar environment and may therefore reflect a generalized sedation. The receptor specificity of these differential effects of 5HT-1 and 5HT-2 agonists in this paradigm was tested by assessing the ability of selective 5HT-2 antagonists to block the effects of the agonists. A dose of the 5HT-2 antagonist ketanserin which had no effect by itself significantly reduced the behavioral effects of mescaline, DOM, and quipazine. Similarly, the selective 5HT-2 antagonist ritanserin blocked the effect of quipazine. In contrast, ketanserin had no significant effect on the suppression of activity produced by the 5HT-1A agonist 8-hydroxy-2(di-n-propylamino)tetralin (8OHDPAT).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- L L Wing
- Department of Psychiatry, School of Medicine, University of California, San Diego, La Jolla 92093
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50
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Abstract
Drug discrimination is a technique for investigating the stimulus properties of centrally active drugs. Although many studies have employed animals to investigate the stimulus properties of substances used clinically for the treatment of anxiety and depression, it would be a mistake to consider the internal discriminative stimuli as being related specifically to the anxiolytic or antidepressant properties of these drugs. Rather drug cues are better considered as relating to the pharmacological action of classes of compounds. Thus, benzodiazepine cues generalize to other compounds acting at benzodiazepine receptors, but not to substances (anxiolytic or otherwise) acting at 5-HT1A receptors. Similarly, antidepressants with different pharmacological properties, for example the tricyclic imipramine, or the phenylaminoketone buproprion produce distinct, unrelated discriminative stimuli. For this reason, the limits of drug discrimination techniques for investigating novel anxiolytic or antidepressant drugs should be clearly recognized. Attempts to identify an anxiogenic discriminative stimulus using pentylenetetrazole have also been misguided. In this technique it has proven difficult to separate unequivocally the pharmacological proconvulsant effects of the drug from the psychological construct anxiety. Nevertheless, drug discrimination remains a valuable technique for investigating pharmacological interactions in animals and man.
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Affiliation(s)
- J S Andrews
- Department of Neuropsychopharmacology, Schering AG, Berlin, F.R.G
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